Modifying backbone service instance identifiers based on an identified flow of associated frames

ABSTRACT

In one embodiment, backbone service instance identifiers (I-SIDs) of backbone frames are modified based on flow identification of frames encapsulated therein to induce entropy into the headers of the backbone frames. Backbone packet switching devices use the modified service instance identifier to load balance the corresponding frame through the backbone network. At an exit point of the backbone network, the original backbone service instance identifier (I-SID) associated with a frame encapsulated in a backbone frame is recovered from the modified service instance identifier, with this recovery typically including determining the flow identification of the frame encapsulated in the backbone frame.

TECHNICAL FIELD

The present disclosure relates generally to communicating informationwith remote device over a network.

BACKGROUND

The communications industry is rapidly changing to adjust to emergingtechnologies and ever increasing customer demand. This customer demandfor new applications and increased performance of existing applicationsis driving communications network and system providers to employnetworks and systems having greater speed and capacity (e.g., greaterbandwidth). In trying to achieve these goals, a common approach taken bymany communications providers is to use packet switching technology.

In a Provider Backbone Bridging architecture, customer networks (e.g.,using 802.1q bridging) are aggregated into Provider Bridged networks(e.g., using 802.1ad). These, in turn, are aggregated into ProviderBackbone Bridging networks which use the 802.1 ah frame format. Theframe format employs a MAC tunneling encapsulation scheme for tunnelingcustomer Ethernet frames within provider Ethernet frames across theProvider Backbone Bridging network. A VLAN ID is used to segregate thebackbone into broadcast domains or topologies, and a 24-bit serviceidentifier (I-SID) is defined and used to associate a given customer MACframe with a provider service instance.

BRIEF DESCRIPTION OF THE DRAWINGS

The appended claims set forth the features of one or more embodimentswith particularity. The embodiment(s), together with its advantages, maybe best understood from the following detailed description taken inconjunction with the accompanying drawings of which:

FIG. 1 illustrates an example network according to one embodiment;

FIG. 2 illustrates an example apparatus according to one embodiment;

FIG. 3 illustrates an example process according to one embodiment;

FIG. 4 illustrates an example process according to one embodiment; and

FIG. 5 illustrates an example process according to one embodiment.

DESCRIPTION OF EXAMPLE EMBODIMENTS 1. Overview

Disclosed are, inter alia, methods, apparatus, computer-storage media,mechanisms, and means associated with modifying backbone serviceinstance identifiers (I-SIDs) of backbone frames based on flowidentification of frames encapsulated therein. One embodiment includes:determining a flow identification value derived from one or more fieldsof the header of a particular frame; generating a modulated serviceinstance identifier, which includes: modulating a backbone serviceinstance identifier (I-SID) associated with the particular frame withthe flow identification value to generate the modulated service instanceidentifier; and sending, from a first packet switching device into anetwork, a backbone frame encapsulating the particular frame, with theheader of the backbone frame including the modulated service instanceidentifier. One embodiment includes: receiving, by the first packetswitching device, the particular frame; determining, by the first packetswitching device, the backbone service instance identifier (I-SID)corresponding to the particular frame; and encapsulating the particularframe to produce the backbone frame, with the header of the backboneframe including the modulated service instance identifier.

One embodiment includes: a second packet switching device in the networkcommunicating the backbone frame to a third packet switching device;wherein said communicating includes load balancing the backbone frameacross a plurality of links based on using the modulated serviceinstance identifier as a load balancing value.

One embodiment includes: receiving, by a particular packet switchingdevice, the backbone frame; processing, by the particular packetswitching device, the modulated service instance identifier to generatethe backbone service instance identifier (I-SID); and sending theparticular frame from the particular packet switching device based onthe backbone service instance identifier (I-SID). In one embodiment,said processing the modulated service instance identifier includes:determining the flow identification value from said one or more fieldsof the header of the particular frame, and demodulating the backboneservice instance identifier (I-SID) from the modulated service instanceidentifier based on the flow identification value. In one embodiment,said demodulating the backbone service instance identifier (I-SID) fromthe modulated service instance identifier based on the flowidentification value includes exclusive-ORing the modulated serviceinstance identifier and the flow identification value.

In one embodiment, said one or more fields of the header of theparticular frame include: the source and destination addresses of theparticular frame. In one embodiment, said one or more fields of theheader of the particular frame include: the source and destinationaddresses of the particular frame, and source and destination address ofan Internet Protocol packet encapsulated within the particular frame. Inone embodiment, said modulating the I-SID with the flow identificationvalue to generate a modulated service instance identifier includesexclusive-ORing the backbone service instance identifier (I-SID) and theflow identification value.

One embodiment includes: receiving, by a packet switching device, abackbone frame including a modulated service instance identifier and aparticular frame; processing the modulated service instance identifierto determine a backbone service instance identifier (I-SID)corresponding to the particular frame; and sending the particular framefrom the packet switching device based on the backbone service instanceidentifier (I-SID), or sending of a modified backbone frame based onsaid received backbone frame with the modified backbone frame includingthe backbone service instance identifier (I-SID) and the particularframe.

In one embodiment, said processing the modulated service instanceidentifier includes: determining a flow identification value from one ormore fields of the header of the particular frame, and demodulating thebackbone service instance identifier (I-SID) from the modulated serviceinstance identifier based on the flow identification value. In oneembodiment, said demodulating the backbone service instance identifier(I-SID) from the modulated service instance identifier based on the flowidentification value includes exclusive-ORing the modulated serviceinstance identifier and the flow identification value.

2. Description

Disclosed are, inter alia, methods, apparatus, computer-storage media,mechanisms, and means associated with modifying backbone serviceinstance identifiers (I-SIDs) of backbone frames based on flowidentification of frames encapsulated therein.

Embodiments described herein include various elements and limitations,with no one element or limitation contemplated as being a criticalelement or limitation. Each of the claims individually recites an aspectof the embodiment in its entirety. Moreover, some embodiments describedmay include, but are not limited to, inter alia, systems, networks,integrated circuit chips, embedded processors, ASICs, methods, andcomputer-readable media containing instructions. One or multiplesystems, devices, components, etc. may comprise one or more embodiments,which may include some elements or limitations of a claim beingperformed by the same or different systems, devices, components, etc. Aprocessing element may be a general processor, task-specific processor,or other implementation for performing the corresponding processing. Theembodiments described hereinafter embody various aspects andconfigurations, with the figures illustrating exemplary and non-limitingconfigurations. Note, computer-readable media and means for performingmethods and processing block operations (e.g., a processor and memory orother apparatus configured to perform such operations) are disclosed andare in keeping with the extensible scope and spirit of the embodiments.Note, the term “apparatus” is used consistently herein with its commondefinition of an appliance or device.

Note, the steps, connections, and processing of signals and informationillustrated in the figures, including, but not limited to, any block andflow diagrams and message sequence charts, may typically be performed inthe same or in a different serial or parallel ordering and/or bydifferent components and/or processes, threads, etc., and/or overdifferent connections and be combined with other functions in otherembodiments, unless this disables the embodiment or a sequence isexplicitly or implicitly required (e.g., for a sequence of read thevalue, process said read value—the value must be obtained prior toprocessing it, although some of the associated processing may beperformed prior to, concurrently with, and/or after the read operation).Also note, nothing described or referenced in this document is admittedas prior art to this application unless explicitly so stated.

The term “one embodiment” is used herein to reference a particularembodiment, wherein each reference to “one embodiment” may refer to adifferent embodiment, and the use of the term repeatedly herein indescribing associated features, elements and/or limitations does notestablish a cumulative set of associated features, elements and/orlimitations that each and every embodiment must include, although anembodiment typically may include all these features, elements and/orlimitations. In addition, the terms “first,” “second,” etc. aretypically used herein to denote different units (e.g., a first element,a second element). The use of these terms herein does not necessarilyconnote an ordering such as one unit or event occurring or coming beforeanother, but rather provides a mechanism to distinguish betweenparticular units. Moreover, the phrases “based on x” and “in response tox” are used to indicate a minimum set of items “x” from which somethingis derived or caused, wherein “x” is extensible and does not necessarilydescribe a complete list of items on which the operation is performed,etc. Additionally, the phrase “coupled to” is used to indicate somelevel of direct or indirect connection between two elements or devices,with the coupling device or devices modifying or not modifying thecoupled signal or communicated information. Moreover, the term “or” isused herein to identify a selection of one or more, including all, ofthe conjunctive items. Additionally, the transitional term “comprising,”which is synonymous with “including,” “containing,” or “characterizedby,” is inclusive or open-ended and does not exclude additional,unrecited elements or method steps. Finally, the term “particularmachine,” when recited in a method claim for performing steps, refers toa particular machine within the 35 USC §101 machine statutory class.

Expressly turning to the figures, FIG. 1 illustrates a networkconfigured to operate, or operating, according to one embodiment. Shownare packet switching devices 100, 102, 106 and 108, with network 104also including one or more packet switching devices. Of course, thenetwork connectivity of an embodiment will vary from that shown in FIG.1, but this network provides for the teaching of one or moreembodiments.

In one embodiment, packet switching device 100 (e.g., a customer device)communicates a frame 101 (e.g., Ethernet frame) to packet switchingdevice 102 (e.g., a provider backbone edge bridge), which in turndetermines a backbone frame to encapsulate the received frame 101, withthe backbone frame including forwarding information for use inforwarding through network 104 (e.g., a provider backbone networkincluding backbone core bridges). This determined forwarding informationincludes a backbone service instance identifier (I-SID) associated withthe received frame. The backbone service instance identifier (I-SID) isa typically used to identify a particular customer in a known providerbackbone network.

Rather than use the original backbone service instance identifier(I-SID), one embodiment modifies backbone service instance identifier(I-SID) based on a flow identification derived from one or more fieldsof the received frame in a manner that will allow a subsequent packetswitching device to recover the original backbone service instanceidentifier (I-SID) from the modulated service instance identifier. Thisallows, for example in one embodiment, packet switching devices innetwork 104 to load balance backbone provider frames based on includedmodulated service instance identifiers. When load balancing it istypically desirous that frames of a flow are load balanced in the samemanner so frames traverse a network over a same path as to avoidreordering of frames at the receiving switch. Also, known hashing andother techniques can be used to produce a value based on the flowidentification information which adds entropy when creating themodulated service instance identifier. This typically results in betterload balancing of flows of frames.

Packet switching device 102 sends the resulting backbone frame 103,including the originally received frame and the modulated serviceinstance identifier, into network 104, in which packet switching devicestypically load balance the forwarding of packets based on the modulatedservice instance identifier, with this backbone frame 105 beingcommunicated to packet switching device 106. Note that backbone frame105 is typically the same as backbone frame 103. Packet switching device106 demodulates the modulated service instance identifier to produce theoriginal service instance identifier (I-SID), which may identify acorresponding customer. Packet switching device 106 typically sends,based on the service instance identifier (I-SID), the decapsulate frame107 (e.g., the same frame as frame 101) to packet switching device 108.

Also illustrated in FIG. 1 is a network architecture in which packetswitching devices 100 and/or 108 are aggregating (or other) deviceswhich perform the known encapsulation of received frames into backboneframes (e.g., which include corresponding backbone service instanceidentifiers (I-SIDs)). Thus, in one embodiment, packet switching device102 receives a backbone frame 101 including a backbone service instanceidentifier (I-SID) and encapsulated frame. Therefore, packet switchingdevice 102 does not need to determine this backbone information, butrather, modifies the received backbone service instance identifier(I-SID) based on a flow identified for the encapsulated frame, and sendsout a corresponding backbone frame 103, which includes the modulatedservice instance identifier. Similarly, packet switching device 106receives the corresponding backbone frame 105 and demodulates themodulated service instance identifier to produce the backbone serviceinstance identifier (I-SID) (e.g., the I-SID originally received bypacket switching device 102 in backbone frame 101). In one embodiment,packet switching device 106 sends out frame 107 (e.g., an Ethernetframe/non-backbone frame). In one embodiment, packet switching device106 sends out backbone frame 107 with the original, non-modulatedbackbone service instance identifier (I-SID).

Note that FIG. 1 illustrates processes of sending packets from packetswitching device 100 to packet switching device 108, and from packetswitching device 108 to packet switching device 100 with correspondingoperations performed for sending packets in the desired direction. Also,in one embodiment, packet switching device 102 receives frame 101 (e.g.,an Ethernet frame/non-backbone frame) and packet switching device 106sends out corresponding frame 107 in the form of either a frame 107(e.g., an Ethernet frame/non-backbone frame) or backbone frame 107.

FIG. 2 is a block diagram of an apparatus or component 290 used in oneembodiment associated with modifying backbone service instanceidentifiers (I-SIDs) of backbone frames based on flow identification offrames encapsulated therein. In one embodiment, apparatus or component290 performs one or more processes corresponding to one of the flowdiagrams illustrated or otherwise described herein, and/or illustratedin another diagram or otherwise described herein.

In one embodiment, apparatus or component 290 includes one or moreprocessing element(s) 291, memory 292, storage device(s) 293,specialized component(s) 295 (e.g. optimized hardware such as forperforming operations, etc.), and interface(s) 297 for communicatinginformation (e.g., sending and receiving packets, user-interfaces,displaying information, etc.). These elements can be communicativelycoupled via one or more communications mechanisms 299, with thecommunications paths typically tailored to meet the needs of aparticular application. In one embodiment, apparatus or component 290corresponds to, or is part of, a packet switching device (100, 102, 106,108 or within network 104) of FIG. 1.

Various embodiments of apparatus or component 290 may include more orfewer elements. The operation of apparatus or component 290 is typicallycontrolled by processing element(s) 291 using memory 292 and storagedevice(s) 293 to perform one or more tasks or processes. Memory 292 isone type of computer-readable/computer-storage medium, and typicallycomprises random access memory (RAM), read only memory (ROM), flashmemory, integrated circuits, and/or other memory components. Memory 292typically stores computer-executable instructions to be executed byprocessing element(s) 291 and/or data which is manipulated by processingelement(s) 291 for implementing functionality in accordance with anembodiment. Storage device(s) 293 are another type of computer-readablemedium, and typically comprise solid state storage media, disk drives,diskettes, networked services, tape drives, and other storage devices.Storage device(s) 293 typically store computer-executable instructionsto be executed by processing element(s) 291 and/or data which ismanipulated by processing element(s) 291 for implementing functionalityin accordance with an embodiment.

FIG. 3 illustrates an example process configured to be performed, and/oris performed, in one embodiment typically by a single packet switchingdevice (e.g., a switch or bridge). Processing begins with process block300, and in process block 302, a frame is acquired (e.g., typicallyreceived but also could be created by the packet switching device). Asdetermined in process block 303, if the received frame is not already abackbone frame, then in process block 304, the backbone forwardinginformation (e.g., backbone source and destination addresses, backboneservice instance identifier (I-SID), possibly B-Tag, etc.) isdetermined.

Next, in process block 306, a flow identification value is determinedbased on one or more fields of the received particular frame (e.g., thereceived Ethernet/non-backbone frame, or the encapsulated frame in thereceived backbone frame). A flow is typically identified by an n-tupleof any layer-2, layer-3 or layer-4 information associated with thereceived frame. For example, one embodiment determines this flowidentification value based on the MAC source and destination addresses.When an IP packet is encapsulated in the frame, one embodimentdetermines this flow identification value based on the MAC source anddestination addresses and on the IP source and destination addresses,and possibly further based on UDP or TCP port numbers. Additionally, thevalue(s) of the one or more fields of the received particular frame, andpossibly one or more values from the packet switching device, aretypically hashed or otherwise manipulated to create the flowidentification value in a manner to add entropy. There are numerousalgorithms known for performing such hashing and manipulation to providegood, possibly random or pseudo-random, distribution of values based ondifferent flows of frames and packets.

In process block 308, the modulated service instance identifier isgenerated, which typically includes modulating the backbone serviceinstance identifier (I-SID) with the flow identification value. In oneembodiment, the flow identification value and the backbone serviceinstance identifier (I-SID) have the same number of bits, which areexclusive-ORed to produce the modified service instance identifier.Other techniques can be used to add entropy of the flow identificationvalue to the backbone service instance identifier (I-SID) to create themodulated service instance identifier, from which the original backboneservice instance identifier (I-SID) can be recovered by another packetswitching device.

In process block 310, the backbone frame, with its header including themodulated service instance identifier and the frame encapsulated therein is sent from the packet switching device. In one embodiment, thebackbone frame includes a B-tag. In one embodiment, the backbone framedoes not include a B-tag. In one embodiment, the backbone frame includesa 4-bit time-to-live value (TTL) and 24-bit modulated service instanceidentifier (I-SID). In one embodiment, the backbone frame includes a6-bit time-to-live value (TTL) and a 20-bit modulated service instanceidentifier. In one embodiment, the backbone frame includes a modulatedservice instance identifier having a different number of bits thantwenty or twenty-four bits.

Processing of the flow diagram of FIG. 3 is completed as indicated byprocess block 319.

FIG. 4 illustrates an example process configured to be performed, and/orperformed, in one embodiment typically by a single packet switchingdevice (e.g., a switch or bridge). Processing begins with process block400. In process block 402, a backbone frame, including a modulatedservice instance identifier, is received. In process block 404, theforwarding information for the received backbone packet is determined,which may include load balancing the backbone packet over a set of linksbased on using a modulated service instance identifier as a loadbalancing value to identify a particular link from the set of equal costlinks. The backbone frame is sent accordingly from the packet switchingdevice. Processing of the flow diagram of FIG. 4 is completed asindicated by process block 409.

FIG. 5 illustrates an example process configured to be performed, and/orperformed, in one embodiment. Processing begins with process block 500.In process block 502, a backbone frame, including a modulated serviceinstance identifier, is received. In process block 504, the flowidentification value is determined based on one or more fields of theparticular frame. Note that this operation is typically the same asperformed in process block 306 of FIG. 3 so as to result in the sameflow identification value. In process block 506, the original serviceinstance (I-SID) is determined from the modulated service instanceidentifier based on the flow identification value. A different techniquecan be used to generate the flow identification value other than thatused in process block 306 as long as the original service instance(I-SID) can be recovered from the received modulated service instanceidentifier.

As determined in process block 507, if a backbone frame is to be sentout, then in process block 508, a modified backbone frame, based on saidreceived backbone frame, is sent from the packet switching device withthe modified backbone frame including the backbone service instanceidentifier (I-SID) and the particular frame. Otherwise, if it wasdetermined in process block 507 to send out the particular frame, inprocess block 510, the particular frame is sent from the packetswitching device based on the recovered backbone service instanceidentifier (I-SID). Processing of the flow diagram of FIG. 5 iscompleted as indicated by process block 519.

In view of the many possible embodiments to which the principles of thedisclosure may be applied, it will be appreciated that the embodimentsand aspects thereof described herein with respect to thedrawings/figures are only illustrative and should not be taken aslimiting the scope of the disclosure. For example, and as would beapparent to one skilled in the art, many of the process block operationscan be re-ordered to be performed before, after, or substantiallyconcurrent with other operations. Also, many different forms of datastructures could be used in various embodiments. The disclosure asdescribed herein contemplates all such embodiments as may come withinthe scope of the following claims and equivalents thereof.

What is claimed is:
 1. A method, comprising: determining a flowidentification value derived from one or more fields of the header of aparticular frame; generating a modulated service instance identifier,which includes modulating a backbone service instance identifier (I-SID)associated with the particular frame with the flow identification value,with said modulating including performing a function with operands ofthe backbone service instance identifier (I-SID) and the flowidentification value resulting in the modulated service instanceidentifier with the backbone service instance identifier (I-SID) beingrecoverable from the modulated service instance identifier and the flowidentification value; and sending, from a first packet switching deviceinto a network, a backbone frame encapsulating the particular frame,with the header of the backbone frame including the modulated serviceinstance identifier; receiving, at a particular packet switching device,the backbone frame; processing, at the particular packet switchingdevice, the modulated service instance identifier to generate thebackbone service instance identifier (I-SID), with said processing themodulated service instance identifier including determining the flowidentification value from said one or more fields of the header of theparticular frame and demodulating the backbone service instanceidentifier (I-SID) from the modulated service instance identifier basedon the flow identification value, with said demodulating the backboneservice instance identifier (I-SID) from the modulated service instanceidentifier based on the flow identification value including performingan exclusive-OR operation on the modulated service instance identifierand the flow identification value; and sending the particular frame fromthe particular packet switching device based on the backbone serviceinstance identifier (I-SID).
 2. The method of claim 1, comprising:receiving, at the first packet switching device, the particular frame;determining, at the first packet switching device, the backbone serviceinstance identifier (I-SID) corresponding to the particular frame; andencapsulating the particular frame to produce the backbone frame, withthe header of the backbone frame including the modulated serviceinstance identifier.
 3. The method of claim 1, comprising: a secondpacket switching device in the network communicating the backbone frameto a third packet switching device; wherein said communicating includesload balancing the backbone frame across a plurality of links based onusing the modulated service instance identifier as a load balancingvalue.
 4. The method of claim 1, wherein said modulating the I-SID withthe flow identification value to generate a modulated service instanceidentifier includes performing an exclusive-OR operation on the backboneservice instance identifier (I-SID) and the flow identification value.5. The method of claim 1, wherein said determining the flowidentification value derived from one or more fields of the header ofthe particular frame includes determining the flow identification valuederived from at least two fields of the header of the particular frame;wherein said at least two fields of the header of the particular frameused in determining the flow identification value include both thesource address and destination address of the particular frame.
 6. Amethod, comprising: determining a flow identification value derived fromone or more fields of the header of a particular frame; generating amodulated service instance identifier, which includes modulating abackbone service instance identifier (I-SID) associated with theparticular frame with the flow identification value; and sending, from afirst packet switching device into a network, a backbone frameencapsulating the particular frame, with the header of the backboneframe including the modulated service instance identifier; wherein saidmodulating the I-SID with the flow identification value to generate amodulated service instance identifier includes performing anexclusive-OR operation on the backbone service instance identifier(I-SID) and the flow identification value.
 7. A method, comprising:receiving, at a packet switching device, a backbone frame including amodulated service instance identifier and a particular frame; processingthe modulated service instance identifier to determine a backboneservice instance identifier (I-SID) corresponding to the particularframe, wherein said processing the modulated service instance identifierincludes: determining a flow identification value from at least twofields of the header of the particular frame, and demodulating thebackbone service instance identifier (I-SID) from the modulated serviceinstance identifier based on the flow identification value; and sendingthe particular frame from the packet switching device based on thebackbone service instance identifier (I-SID), or sending of a modifiedbackbone frame based on said received backbone frame with the modifiedbackbone frame including the backbone service instance identifier(I-SID) and the particular frame; wherein said demodulating the backboneservice instance identifier (I-SID) from the modulated service instanceidentifier based on the flow identification value includes performing anexclusive-OR operation on the modulated service instance identifier andthe flow identification value.
 8. A packet switching device, comprising:a plurality of interfaces configured to send and receive packets;memory; and one or more processors perform operations, including:determining a flow identification value derived from one or more fieldsof the header of a particular frame; and generating a modulated serviceinstance identifier, which includes modulating a backbone serviceinstance identifier (I-SID) associated with the particular frame withthe flow identification value, with said modulating including performinga function with operands of the backbone service instance identifier(I-SID) and the flow identification value resulting in the modulatedservice instance identifier with the backbone service instanceidentifier (I-SID) being recoverable from the modulated service instanceidentifier and the flow identification value; wherein the packetswitching device is configured to send a backbone frame encapsulatingthe particular frame, with the header of the backbone frame includingthe modulated service instance identifier; wherein said modulating theI-SID with the flow identification value to generate a modulated serviceinstance identifier includes performing an exclusive-OR operation on thebackbone service instance identifier (I-SID) and the flow identificationvalue.
 9. The packet switching device of claim 8, wherein saidoperations include: determining the backbone service instance identifier(I-SID) corresponding to the particular frame received on one of theplurality of interfaces; and encapsulating the particular frame toproduce the backbone frame, with the header of the backbone frameincluding the modulated service instance identifier.
 10. The packetswitching device of claim 8, wherein said determining the flowidentification value derived from one or more fields of the header ofthe particular frame includes determining the flow identification valuederived from at least two fields of the header of the particular frame;wherein said at least two fields of the header of the particular frameused in determining the flow identification value include both thesource address and destination address of the particular frame.
 11. Apacket switching device, comprising: a plurality of interfacesconfigured to send and receive packets; memory; and one or moreprocessors configured to perform operations, including processing amodulated service instance identifier of a received backbone frame todetermine a backbone service instance identifier (I-SID) correspondingto a particular frame encapsulated within the received backbone frame;and wherein the packet switching device is configured to: send theparticular frame based on the backbone service instance identifier(I-SID), or to send a modified backbone frame based on the receivedbackbone frame with the modified backbone frame including the backboneservice instance identifier (I-SID) and the particular frame; whereinsaid processing the modulated service instance identifier includes:determining a flow identification value from at least two fields of theheader of the particular frame, and demodulating the backbone serviceinstance identifier (I-SID) from the modulated service instanceidentifier based on the flow identification value; and wherein saiddemodulating the backbone service instance identifier (I-SID) from themodulated service instance identifier based on the flow identificationvalue includes performing an exclusive-OR operation on the modulatedservice instance identifier and the flow identification value.
 12. Amethod, comprising: determining a flow identification value derived fromone or more fields of the header of a particular frame; generating amodulated service instance identifier, which includes modulating abackbone service instance identifier (I-SID) associated with theparticular frame with the flow identification value, with saidmodulating including performing a function with operands of the backboneservice instance identifier (I-SID) and the flow identification valueresulting in the modulated service instance identifier with the backboneservice instance identifier (I-SID) being recoverable from the modulatedservice instance identifier and the flow identification value; andsending, from a first packet switching device into a network, a backboneframe encapsulating the particular frame, with the header of thebackbone frame including the modulated service instance identifier;wherein said modulating the I-SID with the flow identification value togenerate a modulated service instance identifier includes performing anexclusive-OR operation on the backbone service instance identifier(I-SID) and the flow identification value.